1. Field of the Invention
The present invention relates to elbow arthroplasty, particularly for canines. More particularly, it relates to a modular elbow replacement prosthesis and a procedure for implantation of the prosthesis.
2. Discussion of Related Art
The canine elbow is a complex hinge joint that moves about its center of rotation in a sagittal plane (sagittal range of motion arc). The distal humerus, proximal ulna, and proximal radius articulate at the elbow in all combinations. The humeroradial and humeroulnar articulations are the main load-supporting pairs. Axial load is transferred through both the humeroradial and humeroulnar articulations while the humeroulnar articulation is also loaded through the trochlear notch of the ulna and trochlea of the humerus by high levering forces exerted by the elbow extensor (triceps) muscles. The radius also rotates internally and externally within the radial notch of the ulna, independent from movement of the ulna. This independent rotation of the radial head allows for the normal pronation and supination that occurs during the canine gait.
Elbow dysplasia (specifically fragmented coronoid process) and the resulting osteoarthritis is the most common orthopedic problem in the canine forelimb. Arthrosis of the elbow in dogs is extremely debilitating with surgical and medical treatment frequently providing only partial and temporary success. Long term treatment success of fragmented coronoid process has been reported at less the 50% with medical management and less than 60% with surgical management. Standard treatment for severe arthrosis of the canine hip is the total hip arthroplasty. Total joint arthroplasty has been successfully performed in the canine coxofemoral joint with success rates reported up to 95%. Total elbow arthroplasty in the dog has not met with comparable success rates.
In dogs, elbow pathology originates on the medial (humeroulnar) compartment of the joint. Medial compartment cartilage erosion results from a fragmented coronoid process, incongruency, and osteochondrosis or osteochodritis desiccans. Severe medial compartment pathology frequently occurs without any significant lesions in the lateral (humeroradial) compartment. Unicompartmental knee replacements have been performed in people for decades. Published long-term clinical results of a unicompartmental knee demonstrated a 98% success rate at 10 years and 95% at 15 years and beyond. Unicompartmental knee patients also benefit from a less invasive procedure with a quicker recovery. There is a need for a unicompartmental elbow athroplasty that treats only the medial compartment of the elbow.
All prior attempts of elbow arthroplasty in the dog have been with systems that were constrained or semiconstrained, bicompartmental total elbow replacements. Unacceptable failure rates for total elbow arthroplasty are a result of treating the elbow as a unicompartmental joint with a constrained prosthesis. Constraint implies some type of mechanical link or coupling between the bones implanted with the prosthesis. Prior elbow replacements have not addressed the normal anatomical movement between the radius and ulna and have constrained this movement with the prosthesis. Ligaments and other soft tissue structures transfer stresses across the joint as they share in load transfer within the joint. Prosthesis constraint to another bone within the joint will transfer those stresses into the implant-bone interface, leading to early implant fixation failure. There is a need for a canine total elbow arthroplasty that recognizes the three compartments of the elbow joint—1) the humeroradial articulation, 2) the humeroulnar articulation, 3) the radioulnar articulation, and allows each to function naturally in a nonconstrained fashion.
Various prostheses and implantation processes have been proposed or used for partial or complete elbow replacement in humans, dogs, or other animals. Given the complex nature of the elbow joint, these prostheses are often complex having many interconnected parts. The implantation processes are similarly complex. They require precise removal of large portions of the bones at the elbow and precise placement of the various components of the prosthesis. Often, the implantation process requires removal of or damage to the ligaments of the elbow, which limits operation of the elbow following the replacement.